I think a search for the son's baptism might be a better place to start. If you can find this parish then you have a starting point to search for the parents marriage, possible siblings etc ..
New Ross could mean that it was the closest town to where Robert and Mary lived - they could have been located in one of the surrounding parishes, or from a different part of Co. Wexford originally.
Other than a manual trawl of all the parishes near to New Ross I think it may be better to wait to see what Co. Wexford records RootsIreland add and see if a baptism shows up for Patrick.
Shane